Acute renal failure (“ARF”) is an abrupt decrease in the kidney's ability to excrete waste from a patient's blood. This change in kidney function may be attributable to many causes. A traumatic event, such as hemorrhage, gastrointestinal fluid loss, or renal fluid loss without proper fluid replacement may cause the patient to go into ARF. Patient's may also become vulnerable to ARF after receiving anesthesia, surgery, α-adrenergic argonists or high dose dopamine or patients with hepatorenal syndrome because of related systemic or renal vasoconstriction. Alternatively, systemic vasodilation cause by anaphylaxis; antihypertensive drugs, sepsis or drug overdose may also cause ARF because the body's natural defense is to shut down “non-essential” organs such as the kidneys. Additionally, reduced cardiac output caused by cardiac shock, congestive heart failure, pericardial tamponade or massive pulmonary embolism creates an excess of fluid in the body. Specifically it has long been known that cardiac dysfunction induces a series of events that ultimately contribute to congestive heart failure (“CHF”). One such event is a reduction in renal blood flow due to reduced cardiac output. This reduced flow can in turn result in the retention of excess fluid in the patient's body, leading for example, to pulmonary and cardiac edema.
The appearance of ARF significantly increases mortality. ICU patients mortality rates for patients without ARF are approximately 20%. However, once ARF is achieved, the mortality rates jump to between 60% and 80%. Preventing ARF in patients at risk but who have not yet had any renal insufficiency will have a dramatic impact on ICU mortality rates.
Chapter 62 of Heart Disease: A Textbook of Cardiovascular Medicine, (E. Braunwald, ed., 5th ed. 1996), published by Saunders of Philadelphia, Pa., reports that for patients with CHF, the fall in effective renal blood flow is proportional to the reduction in cardiac output. Renal blood flow in normal patients in an age range of 20-80 years averages 600 to 660 ml/min/m2 corresponding to about 14 to 20 percent of simultaneously measured cardiac output. Within a wide spectrum of CHF severity, renal blood flow is depressed to an average range of 250 to 450 ml/min/m2.
Previously known methods of treating ARF attributable to congestive heart failure and deteriorating renal function in patients having CHF principally involve administering drugs, including diuretics that enhance renal function, such as furosemide and thiazide; vasopressors intended to enhance renal blood flow, such as Dopamine; and vasodilators that reduce vasoconstriction of the renal vessels. Many of these drugs, when administered in systemic doses, have undesirable side-effects. Additionally, many of these drugs would not be helpful in treating other causes of ARF. Specifically, administering vasodilators to dilate the renal artery to a patient suffering from systemic vasodilation would merely compound the vasodilation system wide.
In addition, for patients with severe CHF (e.g., those awaiting heart transplant), mechanical methods, such as hemodialysis or left ventricular assist devices, may be implemented. Mechanical treatments, such as hemodialysis, however, generally have not been used for long-term management of CHF. Such mechanical treatments would also not be help for patients with strong hearts suffering from ARF.
Advanced heart failure (“HF”) requires the combination of potent diuretics and severe restriction of salt intake. Poor patient compliance is a major cause of refractoriness to treatment. On the other hand, as renal urine output decreases with reduced renal perfusion, in the event of dehydration, the required diuretic dosages increase.
Recent work has focused on the use of intra-aortic balloon pumps (IABPs) to divert blood flow into the renal arteries. One such technique involves placing an IABP in the abdominal aorta so that the balloon is situated slightly below (proximal to) the renal arteries. The balloon is selectively inflated and deflated in a counterpulsation mode so that increased pressure distal to the balloon directs a greater portion of blood flow into the renal arteries.
In view of the foregoing, it would be desirable to provide methods and apparatus for treating and managing ARF without administering high doses of drugs or dehydrating the patient.
It further would be desirable to provide methods and apparatus for treating and managing ARF by improving blood flow to the kidneys, thereby enhancing renal function. Specifically, a system which could be used for all ARF patients during critical treatment times would be beneficial. In particular, a system which could be placed easily in a patient during emergency or critical care without the need for surgery or X-ray fluoroscopy guidance would be useful to all patients in danger of ARF.
It also would be desirable to provide methods and apparatus for treating and managing ARF that permit the administration of low doses of drugs, in a localized manner, to improve renal function without having an effect system wide.
It still further would be desirable to provide methods and apparatus for treating and managing ARF using apparatus that may be percutaneously and transluminally implanted in the patient.